[PATCH][ARM] Implement vectorizer cost hooks

[Richard Earnshaw]

On 05/02/13 18:18, Christophe Lyon wrote:
> Hi,
>
> Following the discussion about "disable peeling" [1] a few weeks ago,
> it turned out that the vectorizer cost model needed some
> implementation for ARM.
>
> The attached patch implements arm_builtin_vectorization_cost and
> arm_add_stmt_cost, providing default costs when aligned and unaligned
> loads/stores have the same cost (=1). init_cost and finish_cost still
> use the default implementation (I noticed that x86 has chosen to
> duplicate the default implementation without changing it, why?)
>
> Benchmarking shows very little variation, expect a noticeable +1.6% on coremark.
>
> If this is OK, we can then discuss how to disable peeling completely
> when aligned and unaligned accesses have the same cost (and thus where
> peeling is a loss of performance). I think adding a new hook is
> necessary, since target descriptions may use different models for
> these costs (eg x86 makes no difference between unaligned loads and
> unaligned stores).
>
> Thanks,
>
> Christophe.
>
> [1] http://gcc.gnu.org/ml/gcc/2012-12/msg00036.html
>
> 2013-02-05  Christophe Lyon <christophe.lyon@linaro.org>
>
>          * config/arm/arm.c (arm_builtin_vectorization_cost)
>          (arm_add_stmt_cost): New functions.
>          (TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST)
>          (TARGET_VECTORIZE_ADD_STMT_COST): Define.
>          (struct processor_costs): New struct type.
>          (default_arm_cost): New struct of type processor_costs.=
>

Christophe,

Thanks for the patch.  This is mostly OK, but please can you make the 
following changes.

+struct processor_costs {

Please name this something like cpu_vec_costs.  It's not the only cost 
table in the back-end.

+struct processor_costs default_arm_cost = {	/* arm generic costs.  */

Similarly, use something like default_arm_vec_cost.

+const struct processor_costs *arm_cost = &default_arm_cost;

And here.  But better still, link this through the current_tune table 
rather than introducing a new global.

Finally,

@@ -27256,4 +27272,130 @@ arm_validize_comparison (rtx *comparison, rtx 
* op1, rtx * op2)

  }

+/* Vectorizer cost model implementation.  */


Please put the patch in a more suitable location rather than just 
dumping it at the end of the file.  There are already numerous functions 
related to costs that are mostly grouped together.  I suggest this goes 
near the rtx_costs code.

R.